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Flexor pollicis longus

The flexor pollicis longus (Latin: musculus flexor pollicis longus) is a long muscle of the upper limb that stretches between the radius and the distal phalanx of the thumb. It is one of the deep muscles of the forearm that is located in the anterior compartment. Together with the flexor digitorum profundus, this deep flexor of the forearm lies in the third muscle layer.

Flexor pollicis longus
OriginAnterior surface of radius, interosseous membrane of forearm
InsertionBase of distal phalanx of the thumb
Action Flexion of thumb, flexion of phalanges at first metacarpophalangeal and interphalangeal joints, flexion of wrist
Innervation Anterior interosseous branch of median nerve (C7, C8)
Blood supply Anterior interosseous and radial arteries



The flexor pollicis longus muscle originates from the proximal anterior surface of the radius and interosseous membrane of the forearm.



Distal fibers of the flexor pollicis longus form a flattened tendon that reaches the thumb via the carpal tunnel. The tendon of the muscle inserts on the base of the distal phalanx of the thumb.



The flexor pollicis longus muscle provides the flexion of the thumb and flexion of the phalanges at the metacarpophalangeal and interphalangeal joints of the first finger. Also, it assists in the flexion of the wrist at the wrist joint.



The flexor pollicis longus is innervated by the anterior interosseous branch of the median nerve (C7, C8).


Blood supply

The medial aspect of the flexor pollicis longus muscle receives arterial blood supply from the anterior interosseous artery that arises from the common interosseous artery. The lateral part of the muscle is supplied by the radial artery - a branch of the brachial artery.